As the Shielded Casting feat works with light shields would it be reasonable to replace line if not char_editor.has_feat(feat_shield_proficiency): in scr\feats\Shielded Casting.py with if not char_editor.has_feat(feat_shield_proficiency) and not char_editor.has_feat("Light Shield Proficiency"): Especially as Warmage seems to be the class which would make the greatest use of this feat?
Shielded Casting is to prevent attacks of opportunity when casting while wearing a shield. It's separate from spell failure.